1. The Field of the Invention
This invention relates to filaments (or fibers) for brushes. More precisely, this invention relates to novel, improved filaments for oral care brushes and to oral care brushes including the novel improved filaments.
2. Description of the Prior Art
Brushing the teeth is universally rcommended as the most effective way to maintain oral hygiene. While there is disagreement as to the most suitable form of brushing, the toothbrush is acknowledged to be the most effective aid in cleaning the teeth. In turn, the cleaning effectiveness of a toothbrush is dependent on such factors as the brushing habits of the user, the frequency, intensity and duration of brushing and the quality of the brush filaments. There is considerable debate in the art relating to the features which provide a toothbrush having maximized cleaning effectiveness. These factors include the material, size, shape, strength and resiliency of the brush filament and the length, width and overall shape and area of the brushing surface. Other features affecting the cleaning effectiveness of a toothbrush include the number of tufts (bundles of individual filaments), the number of rows of tufts and the arrangement of the tufts on the brush head. However there is general agreement in the art that wear is a crucial factor which can dramatically diminish the effectiveness of a toothbrush in maintaining oral hygiene. For example, the art recognizes and acknowledges that diminished effectiveness of a toothbrush by wear can result in increased plaque accumulation and increased risks to periodontium tissue.
The degree of wear of a toothbrush is primarily a function of the properties of the filament and the mechanical force applied to the brush during brushing. The degree of wear can also be accelerated to some extent by abrasive materials normally contained in dentifrices. Brush wear results in tearing, splaying, expansion and fraying of the filaments and a decrease in strength and resiliency of the filaments which is manifested by single filaments deviating from their original direction. Moreover, wear is manifested by a change in the overall shape and size of the brushing surface area and by changes in the texture of the filament. While toothbrush wear varies from user to user, studies indicate that the average toothbrush subject to average use has a usefull effective life from about eight to twelve weeks. Thereafter, wear causes sufficient deterioration of the filaments to warrant replacement of the brush in order to assure continued maintenance of effective oral hygiene.
Unfortunately, toothbrushes are not usually replaced regularly and oftentimes are used far beyond their effective useful life. As mentioned, the dental profession has recommended replacement of toothbrushes after about three months of use. However, annual toothbrush consumption figures indicate that toothbrush uses replace their toothbrushes about once a year. The dental profession has made an earnest effort to educate the public about the need to assess the wear of a toothbrush being used to determine if it should be discarded and replaced. However, these efforts have had limited success since the user has the responsibility to remember the condition of a toothbrush which should be discarded and to remember to monitor and continually assess the condition of the toothbrush. Accordingly, a more effective approach is needed to provide reliable means to signal or warn a toothbrush user when a toothbrush has become sufficiently affected by wear that it should be discarded and replaced.
The present invention is designed to provide such means to the toothbrush user so that the user can visually detect a signal indicative of toothbrush wear and replace the worn toothbrush. In the present invention, the signal indicative of wear is provided by the use of filaments having the capability to undergo a change in color in response to wear. U.K. Application Ser. No. 2,137,080 discloses plastic bristles or filaments for brushes which also change color in response to wear. The filaments disclosed in the U.K. Application are composite filaments and include a colored core completely surrounded by an outer cover material having a color different from the core color. In the disclosed filaments, the core is a reinforcing element and is relatively hard and stiff to control the rigidity of the filament while the outer cover material is softer than the core material and is more susceptible to wear. In use, the cover material becomes worn in the area of the rounded end of the filament and peels or breaks off to expose the core color to signal that the brush should be discarded.
The filaments of the U.K. Application are disclosed as useful for toothbrushes, paintbrushes, polishing brushes, hairbrushes or clothes brushes. However use of the disclosed filaments in toothbrushes can present problems and disadvantages. One apparent disadvantage involves the differentials between the costs of manufacturing a composite filament and manufacturing a mono-filament. Another disadvantage arises because the filaments are designed to provide a signal indicative of wear which occurs suddenly since wear causes the cover material to peel or break away from the filament end. When the cover material suddenly peels or breaks away, the hard, stiff core is exposed which could damage periodontium tissue unless the toothbrush is discarded immediately. Additionally, when used for toothbrushes, the filaments must present a close coordination between the degree of wear and use of the filament needed to cause the peeling or breaking away of the cover material and the capability of the cover material to effectively perform the teeth cleaning function. In other words, the sudden occurrence of the signal should closely coincide with the failure of the cover material to continue to effectively perform its assigned cleaning function. According to the U.K. Specification, the close coordination is controlled by adjustment of the thickness of the cover material and/or by adjustment of the material used as the cover material. Control of the coordination by adjustment of the thickness and/or of the material of the cover material requires close, precise monitoring of the application of the cover material to the core and close monitoring of the quality of materials selected to assure that the cover material provides consistenly uniform performance characteristics. These features can add to the overall costs in manufacturing composite filaments.